Straw choppers are used in agriculture for comminuting crop residues, particularly straw, ejected from a separating device of a combine harvester. The comminuted straw is then distributed by straw guiding plates and/or driven conveying devices across the working width of the harvester head and is intended to be biologically degraded there in order to serve as fertilizer for subsequent crop plants.
Conventional straw choppers comprise a rotor on which suspended chopping blades are mounted. The chopping blades comminute the straw in cooperation with stationary counter-blades, which are usually arranged to be adjustable in position in order to be able to adapt the degree of comminution of the straw to the respective requirements and conditions (See, for example, U.S. Pat. No. 4,612,941 A).
If the straw is to be comminuted even more finely, in order to be biologically degraded more quickly and thoroughly, a so-called straw dam can be brought into an operating position downstream of the counter-blades in which operating position it cooperates with the chopping blades.
This straw dam extends from the housing of the straw chopper at least approximately radially inward. In this operating position, straw accumulates on the upstream side of the friction dam and is further comminuted by the chopping blade when the accumulated straw is conveyed over the straw dam by the chopping blades.
In its operating position, the straw dam is situated just outside the envelope circle of the chopping blades, particularly if it has a straight top edge, or can even penetrate into the envelope circle of the chopping blades if it is provided with notches through which the chopping blades pass. The straw dam can be brought into an inactive non-operating position by being pulled radially outward from of the straw chopper housing, or pivoted about its longitudinal axis and laid flat on the adjacent region of the straw chopper housing.
In the prior art, the counter-blades and the straw dam are adjusted independently of one another. Therefore, two levers or the like must be operated for manual adjustment, and two buttons or switches must be operated from the cab in order to adjust the counter-blades and the straw dam. Therefore a double mechanical effort is necessary for the adjustment and opens the possibility of erroneous operation, because using the straw dam without the counter-blades can hardly lead to the desired effect, but only to wear and tear on the straw dam and to clogging.
The problem addressed by the invention is considered to be the provision of a straw chopper in which the aforementioned disadvantages are not present or are present only in a reduced form.